PURPOSE: To oxidize a hydrocarbon with molecular oxygen in high activity and efficiency without using a reducing agent by using a catalyst containing a heteropolyanion.

CONSTITUTION: A hydrocarbon such as butane or cyclohexane is oxidized with molecular oxygen preferably at 20-100°C in the presence of a catalyst containing a heteropolyanion expressed by formula SiW9Fe2MeO37 (Me is Fe, Ni, Cu, Co or Mn) (preferably SiW9Fe2O37 or SiW9Fe2NiO37). The oxidization reaction is preferably carried out while slowly supplying an electron-donative additive such as pyridine to the heteropolyanion to remarkably improve the conversion. The heteropolyanion can be produced e.g. by adding an aqueous solution of Fe(NO3)3.9H2O to an aqueous solution of CH3COONa.3H2O and adding Na10[SiW9O34].18H2O to the obtained solution to effect the reaction of the components.